Packaged adhesive

ABSTRACT

An adhesive mixture comprising a multiplicity of contiguous deposits of a curable but uncured fluid resin and a fluid curing agent for the resin, said deposits being separated by a thin flexible barrier film of cured resin resulting from the interaction between the resin and curing agent.

THE PRIOR ART

It has long been known that a fluid curable resin may be in contact witha fluid curing agent, and both components will remain in their fluidcondition until the resin and curing agent are mixed together. Thisphenomenon is caused by the formation of a very thin barrier filmbetween the resin and the curing agent, resulting from reaction betweenthe resin and curing agent at their contiguous surfaces.

This has been used in the production of self-locking threaded fasteners,where contiguous deposits of a fluid curable resin and of a curing agenthave been made in thread grooves, and the contiguous deposits mixed byengagement with the threads of a mating threaded member. This isdisclosed in Anthony U.S. Pat. No. 3,061,455, and more particularly inmy prior U.S. Pat. Nos. 4,059,136 and 4,081,012, where adjacent threadgroove convolutions or portions thereof receive the fluid curable resinand the curing agent therefor. In Johnson U.S. Pat. No. 2,939,805,superimposed layers of curable resin and curing agent were deposited ina thread groove, where a "polymeric membrane was substantiallyimmediately formed between the two coatings".

In addition, pressure activated adhesives were formed bymicro-encapsulated fluid curable resin in a fluid curing agent asdisclosed in Deckert et al U.S. Pat. No. 3,746,068.

BRIEF SUMMARY

The present invention relates to a fluid, self-curing or settableadhesive for general application. The adhesive comprises a mixture of amultiplicity of small, discrete, contiguous deposits of a first fluidcomprising a fluid uncured but curable resin, and a second fluidcomprising a fluid curing agent for the particular resin. The contiguousdeposits are separated by a thin, flexible, rupturable protectivebarrier film formed in situ by the reaction by the fluid resin and thefluid curing agent initially in contact therewith.

Formation of the film as to thickness and uniformity is controlled bychilling the deposition, and holding it at reduced temperature, forexample, -10° F., overnight. Variations in temperature or in time andtemperature will vary the thickness and strength of the film.

In a simple example, the resin and curing agent may be simultaneouslysupplied through adjacent nozzles to create a mass of the mixture. Inone embodiment of the invention, the resin is supplied in a series ofpulses, as separate deposit of resin or agent by sequential pumpstrokes, so that each stroke produced is separated by the barrier film.Alternatively, the resin and curing agent may be supplied throughadjacent nozzles as continuous, side-by-side contiguous deposits onto anadvancing thin tape. Preferably the nozzles are rotated about an axisextending along the path of advance of the tape, so that a continuousrope-like deposit of separate strands results. A protective cover tapeis applied over the deposit. The tapes are heat sealable, and sealingseams are provided along the edges of the tapes, and at short intervalsacross the tapes. This displaces the resin and curing agent between thetapes and produces a series of severable sealed packets, in which thesealed globules may be ruptured by kneading the packet, and theintimately mixed resin and curing agent squeezed out through an openingprovided by cutting a corner from the packet.

The fluid resin globules may of course be controlled as to size by theamount supplied by each pulse or "shot" of the fluid supplied to themixture. The controlling factors are that the individual coated depositsmust be large enough so that only a minor portion thereof is reacted toproduce the barrier film. In general terms, the individual sealeddeposits are substantially larger than well known micro-encapsulatedmaterial, preferably several times larger, but small enough tofacilitate intimate mixing with the curing agent when the globules areruptured. The individual globules may be a few (1-5) mm in a transversedirection, and the barrier film of a thickness represented by only a fewmolecules.

DESCRIPTION OF THE DRAWINGS

FIGS. 1-3 represents a magnified different cross sections of the fluidadhesive.

FIG. 4 is a plan view of a continuous tape incorporating the adhesivemixture.

FIG. 5 is a perspective view of apparatus for producing an elongatedseries of packets of the adhesive mixture.

COMPLETE DESCRIPTION

The present invention relates to an adhesive which is a mixture ofdifferent fluids. One of said fluids comprises an uncured, curable fluidresin, such for example, as an epoxy resin. Another of said fluids isfluid curing agent for the selected resin, such for example, as an aminewhen the resin is epoxy, as is well understood in the art.

The mixture is in the form of a multiplicity of small, discrete,contiguous deposits of the different fluids, in which adjacent depositsare separated by a thin, flexible, rupturable barrier film formed of thecured resin as reacted by the fluid curing agent in the mixture.

The specific shape and size of the separate deposits is not directlyobservable, but may be inferred from the method of deposition.

In one embodiment of the invention, deposition of the two fluids is madesimultaneously, as by forcing the fluids through adjacent nozzles tocreate mass, when the fluids, or at least the resin, is forcedintermittently into the mass, the resulting deposits may be in the formof small, discrete bodies which are aptly described as globules. This isnot intended to imply spherical or even roughly spherical deposits. Thedeposits may be random and irregular, and in some cases elongated moreor less continuous strands. In a second embodiment of the invention, thephysical shape of the deposits may be the result of forcing continuousstream, uniform or pulsating, of the different fluids onto a movingbelt, and where the contiguous nozzles through which the fluids areforced are rotated as a unit about an axis generally parallel to thepath of advance of the belt, the resulting deposit may be likened to arope formed of twisted strands.

The specific size of the different deposits may vary widely, but theessential factor is that the thickness of the barrier film shall beextremely small compared to the transverse dimension of the adjacentdeposits which are separated by the film. The film should be onlysufficiently thick to terminate curing of the resin as a result ofcontact with the fluid curing agent. The size of the discrete depositsof fluids is limited by the ability of the barrier films to maintainseparation of the contiguous deposits of different fluids. Thetransverse dimension of the deposits, and particularly the resindeposits, is probably 1-5 mm. and larger deposits will ordinarily dividespontaneously.

The fluids are referred to as fluids, and results may be controlled byseparately controlling the fluidity or viscosity of the fluids. This inturn may be controlled in part by controlling the temperature of thefluids at the time of deposit. For convenience, this will normally beroom temperature.

However, a critical feature of the present invention is limitation ofthe thickness of the barrier film as formed by reaction between theresin and activator or curing agent, which commences immediately ondeposition. Best results are obtained by immediately chilling of themixture. Chilling to -10° F., and holding this temperature overnight orfor a minimum of about twelve hours, has proved effective to arrest thegrowth of the barrier film. The film as thus formed is of more uniform,minimum thickness. After the chill treatment, the mixture is no longeraffected by relatively high temperatures, as for example 115° F.

A further reason for chilling the deposited mixture after deposition isnoted. Where the specific gravity of the uncured fluid resin and fluidcuring agent are different, relative movement therebetween under theinfluence of gravity may produce a further mixing which tends to causeexcessive curing of the resin. This is prevented by prompt chilling ofthe mixture, as previously described, until the formation of theprotective film is complete. Good results are obtained by cooling toabout -10° F. for about 12 hours, and film thickness can be controlledby variations in time and temperature.

In FIG. 1 there is illustrated a mass 10 of the adhesive mixture, inwhich a multiplicity of discrete deposits 12 of fluid curable resin areinterspersed in a carrier fluid containing a curing agent for the resin,indicated at 14.

The resin may be any suitable resin, for example, an epoxy resin, andthe appropriate curing agent is selected for the particular resin, suchfor example, an amine for epoxy.

In production excellent results have been obtained by injecting a seriesof "shots" or pulses of both the fluid resin and activator, but in FIG.1 the deposits of resin are illustrated as essentially surrounded by thefluid curing agent. This is for the reason that the surprising resultsobtained are explained by the formation of an extremely thin barrierfilm of cured resin enclosing each separate deposit of resin, producedby the interaction between the resin and curing agent, which leaves theenclosed deposits substantially as irregular globules or bodiessurrounded by the curing agent, and terminates the reaction between theresin and agent.

FIG. 2 represents a cross-sectional view of a differently depositedmixture. Here irregularly shaped deposits 15 represent deposits ofresin, and contiguous irregularly shaped deposits 16 represent depositsof the curing agent. It will be understood that the single linesseparating areas 15 and 16 represent the cured barrier film.

In FIG. 3, the elongated strands 17 and 18 separately represent thefluid resin and curing agent, and the random arrangement suggested inthis figure follows from rotation of a nozzle head with a plurality ofcontiguous nozzles through which fluid resin and curing agent areseparately fed, either uniformly or in "pulses".

The proportions of resin and curing agent are determined by the quantityof agent required to effect a cure of all of resin in the mass.

The minimum size of the deposits is such as to leave an effective amountof resin in fluid state within each deposit, and this in turn isdetermined in part by the thickness of the protective barrier film ofreacted resin which is effective to terminate the reaction. In general,this film may be extremely thin, as for example measured in microns. Thedeposits of resin may be of a size determined by drop formation inaccordance with the surface tension thereof, or they may besubstantially larger.

The deposits, enclosed by the barrier film as described, may becontrasted with known micro-encapsulated resins by the fact that theenclosure is a film of cured portions of the uncured resin enclosedthereby, that the barrier film is much thinner than knownmicro-encapsulating material, that the barrier film is extremelyflexible and readily rupturable, and that the enclosed deposit can bemaintained only in the fluid mixture as contrasted wtihmicro-encapsulated material in which the micro-capsules areindependently self-supporting.

A further sharp distinction between the adhesive mixture of the presentinvention, and a mixture of pre-formed micro-capsules of uncured resinin a fluid carrier comprising a curing agent, is that the encloseddeposits of the present invention are formed in situ by in effectinjecting small masses or deposits of resin and curing agentsimultaneously into a fluid mass so that the enclosing film which limitspolymerization of the curable resin, is formed of cured resin resultingfrom interaction between the resin and curing agent.

The novel adhesive mixture lends itself to deposition into enclosuressuch as the recess in a wire nut disclosed for example in Stockwell U.S.Pat. No. 2,825,750, after which the deposited mixture can be protectedby a cover film of polyvinyl alcohol.

It also lends itself to production of sealed packets in which themixture retains its overall fluidity for long periods. Such packets maycomprise spaced sheets of flexible material, such for example as heatsealing polyethylene, having a thickness of about 2 mils, for example.To use, the individual packet may be manually kneaded to rupture thefilms enclosing the individual globules of uncured resin and to mix thefluid resin intimately with the curing agent. Thereafter, the adhesivemay be squeezed from an opening in the packet, produced for example bycutting or tearing a corner therefrom. The application of the adhesiveis accomplished by the user without it coming in contact with his hands.

A specific embodiment in accordance with the foregoing was produced byforming envelopes of polyethylene sheet material about one inch squarewith one edge open. Into these envelopes three or four substantiallysimultaneous injections of fluid uncured epoxy resin and a fluid amineepoxy curing agent were made. The openings in the envelopes were thenheat sealed and promptly chilled to greatly retard curing of the resin.The product was found to retain the adhesive in fluid condition for longperiods. It was found that heating the packets to about 115° F. afterchilling had no harmful effect, and the packet contents remained fluid.

This provides a highly useful product, in which the packet can bekneaded while sealed for mix, and then dispensed to the job via aclipped corner. It avoids the messy "two bottle" or "two tube" packagingwhich get progressively gunkier as they are repeatedly used. It providesa neat, disposable, single pack for any curable resin or equivalentmaterial the market dictates as suitable.

In FIGS. 4 and 5, there is diagrammatically illustrated apparatus forproducing the sealed packets, and an elongated series of interconnectedpackets.

Here, a lower tape 20 preferably transversely cupped of a thin heatsealable material, such as 2 mil polyethylene, is advanced and onto it,as through two or more adjacent nozzles 22, 24 are continuously appliedcontiguous streams of uncured fluid resin and fluid curing agent.Preferably, the nozzles are rotated about an axis extendinglongitudinally of the tape 20, and thus produce in effect a rope ortwisted strands of resin and curing agent as seen in FIG. 3. The curingagent is provided at a rate sufficient to in effect envelope the strandsof resin, and forms a barrier film of cured resin surrounding the resindeposits to limit the curing reaction, leaving a quantity of fluidcuring agent sufficient to cure the remainder of the resin when mixedtherewith.

A cover tape 26 of heat sealable polyethylene is applied over thedeposit of resin and curing agent on the bottom tape, and the materialadvanced beneath a heated roller or the like, effective to providesealed edge areas 28, and transverse sealed areas 30. The application ofpressure to the sealed areas displaces the fluid deposit, and providesfor an effective heat seal.

In FIG. 5, there is diagrammatically shown apparatus for producing theseries of packets shown in FIG. 2. A conveyor 40, movable on rollers 42receives the lower tape 20 from a supply roll 44. The contiguouspreferably continuous deposits of uncured fluid resin and the fluidcuring agent therefor are made through nozzles 22, 24 preferablyconnected to a rotatable manifold 46, supplied by conduits 48, 50. Thedeposited material is thus in the form of sensibly twisted continuousstrands, in which the curing agent is sufficient to substantiallyenvelop the strand of resin.

A cover strip or tape 26 is fed from a supply roll 52 and overlies thedeposited material.

A patterned, heated roller 54 is provided having at its edges continuousraised areas 56 with spaced transverse areas 58. Areas 56 provide thecontinuous edge seals 28. The areas 58 displace the deposited materialfrom between tapes or strips 20 and 26, and form the transverse sealedareas 30. The adhesive mixture is thus trapped in sealed envelopes 60,as seen in FIG. 4.

The elongated structure is severed into suitable length and ispreferably chilled or cooled before or after severing, to insurestability of the enclosed globules 12 until the curing of the surfacesof the globules is complete.

Alternatively, a pre-formed mixture of fluid curing agent containing theenclosed globules of uncured resin may be deposited on tape 20,exercising care that the enclosed deposits of resin are not ruptured.

It is essential that the enclosed globules may be ruptured by a manualkneading operation, but until such operation, retain the uncured resinin fluid condition together with the fluid carrier which comprises thecuring agent.

An alternative to the soft kneadable packets is the provision of themixture in collapsible tubes. In this case, the nozzle of the tubethrough which the fluid mixture is dispensed, is restricted and suitableshaped as for example, reticulated to ensure rupture of the filmsenclosing the globules of uncured resin and thorough mixing with thecuring agent as the material is forced through the nozzle.

In order to prevent or minimize mixing of the uncured resin and fluidcuring agent, it may be desirable to control the temperature conditionsunder which the adhesive mixture is prepared. Thus, for example, whendepositing the uncured fluid resin and the fluid on the advancing tape,the materials may be water cooled to about 50° F. so that the top filmcan be laid on and heat sealed as described as the assembly advances.

The fluid resin and curing agent may be supplied continuously in asuccession of "shots", as the tape advances, and where the contiguousnozzles are rotated as previously described, a "marblized" mixtureresults, where discrete elongated deposits of the resin, each enclosedin a thin barrier film of the cured resin, are distributed throughoutthe fluid curing agent.

When the specific gravity of the uncured resin and the fluid curingagent are different, relative movement therebetween under the influenceof gravity may produce a further mixing action which tends to causeexcessive curing of the resin. This may be prevented by cooling orchilling the mixture, as previously described, until the action offorming a protective barrier film about the deposits of resin iscomplete. Good results have been accomplished by cooling the mixture toabout -10° F.

What is claimed is:
 1. A fluid adhesive mixture of different fluids inwhich one of said fluids comprises an uncured, curable fluid resin andanother of said fluids comprises a fluid curing agent for said resin,said mixture being in the form of a multiplicity of small discrete,contiguous deposits of the different fluids in which adjacent depositsare separated by a thin flexible rupturable barrier film formed of thecured resin as reacted by the fluid curing agent.
 2. A mixture asdefined in claim 1 in which one of said fluids is in the form ofdiscrete, irregular, random globules.
 3. A mixture as defined in claim 1in which said one fluid is the fluid resin.
 4. A mixture as defined inclaim 1 in which one of said fluids is in the form of elongatedcontinuous strands.
 5. A mixture as defined in claim 4 in which said onefluid is the fluid resin.
 6. A mixture as defined in claim 1 in whichsaid deposits are elongated, twisted deposits.
 7. A mixture as definedin claim 1 in which said deposits are made simultaneously.
 8. Incombination, a fluid adhesive mixture of different fluids in which oneof said fluids comprises an uncured, curable fluid resin and another ofsaid fluids comprises a fluid curing agent for said resin, said mixturebeing in the form of a multiplicity of small discrete, contiguousdeposits of the different fluids in which adjacent deposits areseparated by a thin flexible rupturable barrier film formed of the curedresin as reacted by the fluid curing agent, and container means in whichsaid mixture is received.
 9. A combination as defined in claim 8 inwhich said deposits of resin are enclosed by barrier films to providesealed cells of resin, and said container means is a flexible,collapsible envelope to provide for rupture of the sealed cells of resinby kneading and dispersal of the resin throughout the fluid curing agentand dispensing from the envelope through an opening therein.
 10. Acombination as defined in claim 9 in which said envelope is a smallpacket containing sufficient resin and curing agent for a simpleapplication.
 11. A combination as defined in claim 8 in which saiddeposits of resin are enclosed by barrier films to provide enclosedresin cells, and said container is a collapsible tube having arestricted outlet opening effective to rupture the enclosed resin cellsand to intimately intermix the fluid resin and fluid curing agent as themixture is expelled by pressure on the tube.
 12. The method of forming aself-curing adhesive mixture which comprises making a multiplicity ofsubstantially discrete deposits of a fluid curable resin and a fluidcuring agent, retaining the deposits in deposited form until interactionbetween the resin and curing agent forms very thin barrier films betweenadjacent deposits of resin and curing agent and chilling the deposits tocontrol the thickness of the barrier formation.
 13. The method asdefined in claim 12 in which the chilling is to about -10° F.
 14. Themethod as defined in claim 12 in which the chilling is for a minimum ofabout 12 hours.